Typical prior art solar collectors are disclosed in GB-A-2023804 and U.S. Pat. No. 4,311,131. These collectors comprise a housing within which is located an absorber. The absorber comprises a plate through which heat is transferred to the working or heat transfer fluid contained in an attached tube. AU-B-537408 describes a solar collector comprising an envelope and an absorber within the envelope, the absorber likewise comprising means by which heat is transferred to the heat transfer fluid.